This invention relates to p53 protein and variations thereof, and more particularly relates to antibodies to such variations.
The p53 gene which encodes for p53 protein is defective in over half of all human cancers. It is furthermore significant because introduction of a normal p53 gene into a variety of cancer cells arrests their growth. Thus, defects in the p53 gene product (that is, the p53 protein) are common in many cancers and, if corrected, could inhibit cancer cell growth. In many human cancers, the p53 protein is inactive because of mutation of the p53 gene. Replacement of a single amino acid can be sufficient to change the normal folding of the p53 protein, making it inactive as a growth control gene. In certain cells, the folding of a mutant p53 protein can be stabilized in the normal conformation by binding to cellular factors, suggesting that it may be possible to create peptides which bind to p53 protein and cause it to be maintained in the normal conformation (conformations are forms of a protein created due to folding; conformations can change without (or with) changes in amino acid sequence). The normal conformation has the tumor suppressor effect. Cells expressing primarily mutant p53 conformation give rise to aggressive tumors at high frequency while cells which primarily express p53 protein in a normal conformation give rise to slow-growing tumors at low frequency.
To date, many studies of p53 protein and its function have relied upon a specific (PAb421) antibody thereto. Most p53 proteins studied using in vitro (cell-free) assays of binding to DNA or modulation of transcription have used a p53 protein purified using PAb421, and thus excluding other proteins. While p53 binding detectable to date is sequence specific, it is low in efficiency. A model has been proposed for activation of p53 protein for binding to DNA by modifications at the carboxyl terminus of p53, Hupp et al. (1992) “Regulation of the specific DNA binding function of p53”, Cell 71, 875-886, as shown in FIG. 1. Modifications include proteolysis (loss of carboxyl terminal amino acids, phosphorylation of serine in this region or binding of PAb421 antibody within this region.
It has been shown that p53as RNA exists in normal mouse cells and tissues and in tumor cells (Han et al. (b) (1992), “Alternatively spliced p53 RNA in transformed and normal cells of different tissue types”, Nucleic Acids Res., 20(8), 1979-1981; however, no protein has heretofore been found which is encoded by that RNA.